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Permeability of drywall primer and sealant

bluesolar | Posted in Energy Efficiency and Durability on

Hi all — I regularly see drywall described as vapor permeable if it’s painted with latex paints. This is normally viewed as a good thing if there’s an impermeable barrier on the exterior side of walls – we’re advised against having impermeable barriers on both sides of a wall because it can trap moisture and cause mold.

But standard best practice is to apply primer to drywall before painting. The primer is supposed to fill the pores. That sounds like it might create an impermeable vapor barrier, or at least a much less permeable barrier. When I read about the permeability of latex painted drywall I never see any mention of primer. Does anyone know if drywall is still permeable when primer is used? Is there any data out there?

Thanks.

p.s. There are also drywall “sealants”, or combo primer + sealant products in wide use. A sealant sounds like it would make something impermeable, by definition, so I’m also interested in any information you have on permeability after drywall sealant is used.

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Replies

  1. Expert Member
    MALCOLM TAYLOR | | #1

    Bluesolar,

    Drywall has a permeance of 50
    Ordinary primer takes it to 5
    Vapour-Retarder primer is 0.5 to 0.9
    Two coats of latex paint 5

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